Masking Agent blocks OS and CPU information from being revealed on the Internet

Your web browser sends information about your system whenever it connects to web services on the Internet. Just open Ghacks' quick IP checker and you will notice that the host can identify your IP address, web browser that you are using, and operating system that you have installed.

Most of the time, it is not necessary that this information is submitted at all. While there are specialized services out there that parse the user agent to determine if the browser and operating system are supported, most Internet sites do not make use of these techniques nor require them to function.

That does not mean that the information are not used. A quick check of the user agent may display different versions of the same web page. Back in 2012 it became known for instance that the online travel agency Orbitz Worldwide is showing customers that use Apple Macintosh systems different and sometimes higher priced travel options than customers who use Windows PCs.

But user-agent information can also be abused my malicious scripts. If a vulnerability is known to only affect a certain operating system version, one could create a script that checks the connecting user's operating system by parsing the user-agent to attack if the information match the vulnerability profile.

Masking Agent

The Firefox add-on Masking Agent replaces OS and CPU information with custom text so that websites cannot use the information anymore. This works well on most websites you connect to, but may be problematic on some that use the information actively as part of their service.

The default replacement text is masking-agent, but you can modify that to anything you like in the options the add-on makes available. Changing text protects the information from being used by websites you connect to.

Note: If you select a unique replacement text, it may actually be easier for websites that use fingerprinting to track you. It is therefore suggested that you do not select a unique replacement text here.

Once you have installed the extension in Firefox, you will notice that it will protect the user agent information and replace them with the chosen text.

Closing Words

If you want to reduce the chance of being fingerprinted effectively while you are browsing the Internet, then Masking Agent may be an option to do so. It does not prevent other means though, like identifying you based on the IP address, but that's something that you can take care of easily as well.

The add-on lacks a blacklist that you can use to disable it on select properties that require correct user-agent information to function.

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About Martin Brinkmann

Martin Brinkmann is a journalist from Germany who founded Ghacks Technology News Back in 2005. He is passionate about all things tech and knows the Internet and computers like the back of his hand.You can follow Martin on Facebook, Twitter or Google+

IP address remains the first referrer (see proxy, vpn …) but the add-on described here calls my attention should it be only for “[…] user-agent information can also be abused my malicious scripts. […]” which is enough in itself, as before privacy is security.

Look out for websites behaving strangely once you change the agent text – for example, under Firefox without an OS mentioned, Google’s Calendar site defaults to the mobile version. I eventually settled on:

Mozilla/5.0 (Windows) Gecko/20100101 Firefox/24.0

This gave me full functionality of Calendar back, and looks generic enough.

You need to remember that many sites legitimately use this info to tailor the website and what functionality you can support in the browser you’re using.

just want to point out that this add on doesnt work well with Unity Webplayer. Which makes sense because the webplayer needs to know your OS/browser, but all it’s reading is ‘masking agent’.

basically, when you open a unity webplayer game (http://www.a10.com/multiplayer-games/cs-portable) with unity installed, the player does not detect whether unity is installed or not, just prompts you to install. after disabling and uninstalling the addon it stil does not work. why? because the extension doesnt clean up well

This browser extension was causing me considerable problems with Yahoo.com. Once I found a agent string it liked, it’s done much better. But, if your agent string is too individualistic, it just becomes an easy identifier.

About gHacks

Ghacks is a technology news blog that was founded in 2005 by Martin Brinkmann. It has since then become one of the most popular tech news sites on the Internet with five authors and regular contributions from freelance writers.